1. Field of the Invention
The present invention relates to an article having an insulation abrasion-resistance coated layer, such as a glass ceramic layer coated thinly on the surfaces of a bearing of a small-size motor, of a bearing of an ultrasmall-size motor or on a metallic base body of the sliding portion of a mechanical seal which coated article has insulation and abrasion-resistance characteristics.
2. Description of the Prior Art
When the insulation abrasion-resistance layer is applied on a sliding portion of a bearing of the small-size motor, the effect of the present invention is considerable. Thus, the bearing of a small-size motor will be described in detail by way of an example as a description of the prior art.
In recent years, the small-size motor is used not only for household and industrial use, but also for ultrasmall size under the social lighter, thinner, shorter, smaller demands, thus increasing the ratio of the coreless motor. FIG. 7 shows a cross-sectional view of a coreless DC motor.
In FIG. 7, a shaft 5 whose tip end is formed circular is rotatably supported by a sleeve-shaped radial bearing 9 provided on a frame 11. A commutator 7 is mounted, with a plurality of forming windings 6 being integrally formed with the shaft 5 by the plastic forming material 8, to construct a rotor. A magnet 12 is secured to the frame 11 against the forming windings 6. Reference numeral 13 is a yoke. A brush 4 comes into slidable contact against the commutator. A bracket 21 which covers the opening of the end portion of the frame 11 is provided, at the center of the inner bottom portion, with a thrust bearing 20, which is adapted to receive the tip end of the shaft 5.
In the above construction, the shaft 5 is adapted to receive the load of the thrust direction by the thrust bearing 20 when the shaft is rotated through the support by the sleeve-shaped radial bearing 9. The load of which the thrust bearing receives at this time becomes 300 through 600 gr in a system where the thrust load is applied by the use of the magnetic force to prevent the vertical motion of the rotor. In the case of the shaft of 1 through 2 mm in diameter, the diameter becomes approximately 0.2 mm in the thrust bearing contact portion of the tip end, the load per unit area becomes 9.5 through 20 Kg f per cm.sup.2. The thrust bearing 20 which receives the load and rotates at high speeds is likely to extremely wear out. If the bearing is constructed of ceramic material such as partially stabilized zirconia, silicon carbide, alumina or the like, which is superior in abrasion resistance respectively, as a precaution against wearout, the metallic shaft would be inconveniently worn out. Also, it is difficult to redesign the size of the ceramic bearing. It is vulnerable to impacts when it is made thinner and smaller. When the impact resistance is improved, the bearing becomes larger, thus making it difficult to design the ultrasmall type motor. In view of these problems, there is a long demand to produce bearings which are superior in impact resistance, have good abrasion resistance and which have insulation characteristics of 20 through 200 .mu.m.
Table 1 shows the materials in a bearing corresponding that is conventionally used in the art, as well as the abrasion amounts, the impact resistances, and the current change in the amount thereof.
The test conditions of Table 1 are as follows.
1. Test temperature: ambient temperature PA0 2. Revolution number: 2200 rpm PA0 3. Rated output: 0.1 W PA0 4. Voltage: 4.2 V PA0 5. Current value: 100 mA
In Table 1, the .circleincircle. mark shows superior impact resistance, and the X mark shows inferior impact resistance. As shown in the results of Table 1, the bearing materials which are superior in abrasion resistance, impact resistance and insulation resistance are desired.
TABLE 1 ______________________________________ Abrasion Material Amount (.mu.m) Impact Current Name 500 H 1000 H Resistance Value mA ______________________________________ 1 66 nylon 20 40 .circleincircle. 105 2 6 nylon 40 70 .circleincircle. 110 3 Polyacetal 40 70 .circleincircle. 110 4 Zirconia 50 100 X 112 5 Alumina 50 100 X 112 6 Silicon carbide 50 100 X 108 ______________________________________